The present invention relates to a torque sensor that detects a steering torque of a driver and a power steering system using the torque sensor. The present invention is applied to the power steering system of a vehicle etc.
For instance, as a related art torque sensor applied to the power steering system of the vehicle, it has been disclosed in Japanese Patent Provisional Publication No. 2004-309463 (hereinafter is referred to as “JP2004-309463”).
A brief explanation of a configuration of the torque sensor in JP2004-309463 will be given here.
The torque sensor has a magnetic member, first and second yoke members, first and second magnetic flux concentrators and a magnetic sensor.
A steering shaft is formed by two shaft members that are relatively rotatably connected to each other through a torsion bar.
The magnetic member is fixed onto an outer periphery of one shaft member of the steering shaft, and has a plurality of magnetic poles in a circumferential direction.
The first and second yoke members are a pair of ring members formed by soft magnetic material, and are fixed onto an outer periphery of the other shaft member of the steering shaft through a certain holder. Each of these ring-shaped first and second yoke members has a plurality of nail portions (fingernails) that extend in a radially inward direction, and the first and second yoke members are arranged so that the nail portions of the first yoke member and the nail portions of the second yoke member face each other (or are opposite to each other) in an axial direction.
The first and second magnetic flux concentrators are each arranged at a part of area, in the circumferential direction, of the first and second yoke members so that the first and second magnetic flux concentrators face each other (or are opposite to each other) between the first and second yoke members in the axial direction. The first and second magnetic flux concentrators are a pair of magnetic flux concentrators by which magnetic field is generated between the yoke members.
The magnetic sensor is accommodated in an air gap formed between the first and second magnetic flux concentrators, and detects magnetic flux that passes between these first and second magnetic flux concentrators.
The torque sensor of JP2004-309463 detects a torque that is inputted to the steering shaft, according to change of the magnetic flux (magnetic flux density) detected by the magnetic sensor.